In an overland conveying system a wire rope is supported and guided by a series of pulleys over which it is dragged at high speed, the rope having only glancing or tangential contact with the pulleys. Examples of such systems are aerial haulage installations and cable belt installations.
One problem with such systems is premature failure of the rope. Another problem is strumming or vibration of the rope (and of the adjacent supporting structures), which may generate an unacceptable level of noise and vibration, which may be troublesome for the local community.
It would be desirable to be able to overcome or mitigate these problems.
We have found that a conventional wire rope 1, as shown in FIGS. 1 and 2, comprising six wire strands 2 (each consisting of wires extending helical around a central wire) extending helically around a core, tends to suffer small lateral displacements as it passes a pulley 3, owing to the undulating surface topography of the rope in the longitudinal direction. The magnitude, d, of the deflection can approach 1% of the rope diameter, depending on the respective profiles of the rope 1 and the pulley 3. We have found that these small rope perturbations can set up vibrations in the rope. These vibrations may represent a source of premature failure due to fatigue. Furthermore, the rope surface may suffer owing to repeated hammering of the pulley on the crowns of the outer wires of the rope.
For the purpose of preventing ingress of abrasives and retaining lubricant, in the field of haulage ropes, it is already known to fill a rope with plastics material. However, if plastics filler elements are introduced into the rope construction, this can cause problems in the manufacture of the rope, because of the difference in physical properties between the (steel) wires and the plastics elements.
It would therefore be desirable to be able to provide a rope which is more easy to manufacture than a conventional plastics filled rope.
The present invention provides a wire rope comprising a central core, a plurality of helical outer strands over the central core, and a plurality of separate pre-formed filler elements, in which one filler element is located between each adjacent pair of outer strands and interlocks with the adjacent strands, the filler elements extending to the imaginary cylindrical envelope of the rope, each filler element consisting of an elastomeric or polymeric material having an oriented molecular structure due to solid-state deformation, the oriented molecular structure being aligned along the filler element.
An oriented molecular structure can be produced by solid state elongation under tension. The oriented structure may be a crystalline or quasi-crystalline structure and may contain whisker-like crystals, whose length will depend on the degree of polymerisation and on the draft (ratio of initial cross-section to final cross-section). If a change in cross-sectional shape takes place at the same time, the oriented structure may have an additional alignment transverse to the longitudinal direction, i.e. there may be biaxial orientation as the material flows in a transverse direction. This is particularly the case if a filler element is formed by solid state drawing of an initially round rod to form a waisted element.
The oriented structure provides the filler element with a high tensile strength and high modulus of elasticity, so that it may be handled in much the same way as a steel element, thereby facilitating manufacture of the rope.